What it is
E100 (curcumin) is the principal yellow-orange pigment extracted from the rhizome of the turmeric plant (Curcuma longa). Pure curcumin is a deep orange-yellow crystalline powder.
Why it matters
Used widely in mustard, curry powders, butter alternatives, margarine, cheeses (including some non-vegan ones), confectionery, and as a natural alternative to tartrazine (E102).
What to do
Always vegan. The closely-related "turmeric" (the whole-spice form, also called E100ii) is likewise vegan. Sometimes blended with carriers like polysorbate or maltodextrin — these are themselves vegan but worth a quick check on more processed products.